Download Fallopia japonica

Fallopia japonica
Taxon
Fallopia japonica (Houtt.) Ronse Decraene var.
japonica
Fallopia sachalinensis (F. Schmidt) Ronse Decraene
Fallopia ×bohemica (Chrtek & Chrtková) J. P. Bailey
Family / Order / Phylum
Polygonaceae / Polygonales / Plantae
COMMON NAMES (English only)
Japanese knotweed s.l.
SYNONYMS
Of Fallopia japonica (Houtt.) Ronse Decraene var.
japonica:
Reynoutria japonica Houtt.
Polygonum cuspidatum Sieb. & Zucc.
Pleuropterus cuspidatus (Siebold & Zucc.) H. Gross
Polygonum sieboldii Reinw. ex de Vries
Polygonum zuccarinii Small
Tiniaria cuspidata (Houtt.) Hedb.
Tiniaria japonica (Houtt.) Hedberg
Of Fallopia sachalinensis (F. Schmidt) Ronse
Decraene:
Reynoutria sachalinensis (F. Schmidt) Nakai
Of Fallopia ×bohemica (Chrtek & Chrtková) J. P.
Bailey
Reynoutria ×bohemica Chrtek & Chrtková
Inflorescence of the hybrid Fallopia × bohemica
Photo: Petr Pysek
SHORT DESCRIPTION
Herbaceous perennials with robust erect stems up to 4 m tall and extensive system of rhizomes, 15–20 m long,
penetrating 2–3 m deep in soil. The invasive knotweeds in Europe include Fallopia japonica var. japonica, F.
sachalinensis, and their hybrid, F. ×bohemica.
BIOLOGY/ECOLOGY
Dispersal mechanisms
Human-transported soil contaminated with rhizomes is the major dispersal mode. Rhizome fragments as small as
7 g fresh weight are able to regenerate, provided a node is present. The hybrid has better regeneration ability than
both parents. Some clones of knotweeds can persist in localities for >130 years.
Reproduction
Knotweeds are functionally dioecious. Flowers are exclusively entomophilous. Only one Fallopia japonica var.
japonica female clone has been introduced and spread over Europe, earning the nickname “world’s largest
female”. The number of flowers per stem exceeds 190,000; they can be fertilized by the pollen of F.
sachalinensis, resulting in F. ×bohemica, or by a congeneric climber F. aubertii, in which case only a low
percentage are fertilized and seedling establishment is inefficient. When seed is produced, the winged achenes
are dispersed by wind and water.
Known predators/herbivores
Palatable to sheep, donkeys, goats, cattle, and horses. House sparrows have been observed removing F. japonica
achenes. The extrafloral nectaries present at the base of the leaves attract predatory ants. Fallopia japonica is a
host to several fungal species. Although herbivorous insects feeding on the foliage of both F. japonica and F.
sachalinensi in Japan can consume >40% of the total leaf area, invertebrate predators do not cause damage in the
invaded range.
Resistant stages (seeds, spores etc.)
HABITAT
Native (EUNIS code)
H6: Recent volcanic features.
Habitat occupied in invaded range (EUNIS code)
E2: Mesic grasslands, E3: Seasonally wet and wet grasslands, F9: Riverine and fen scrubs, FA: Hedgerows, J6:
Garrigue.
Habitat requirements
In its native range, F. japonica is a pioneer species on volcanic slopes. Fallopia sachalinensis occurs in tall-forb
communities at forest edges, avalanche clearings, riverbanks and coastal cliffs, but also colonizes lava flows.
Knotweeds invade disturbed habitats and thrive on a wide range of soils, with pH ranging from 3 to 8.
DISTRIBUTION
Native Range
Knotweeds are native to East Asia, F. japonica to Japan, Korea, Taiwan, and northern China, F. sachalinensis
from Sakhalin Island southwards through Hokkaido to Honshu.
Known Introduced Range
Fallopia japonica is invasive in most European countries, Canada and USA, and reported from Australia and
New Zealand. The distribution of F. sachalinensis in Europe is similar to that of F. japonica but it does not
occur quite as far south. It is also reported from USA, Canada, New Zealand and naturalized in S Japan.
Trend
All three taxa are increasing. The hybrid is competitive and is spreading at a faster rate in Central Europe.
MAP (European distribution)
Known in country
Legend
Known in CGRS square
Known in sea
INTRODUCTION PATHWAY
Fallopia japonica and F. sachalinensis were introduced into Europe as garden ornamentals in the 19th century and soon
escaped from cultivation. Because of its showy blossoms, F. japonica became a popular plant in Victorian gardens of
Europe, winning a gold medal in 1847 from the Society of Agriculture and Horticulture at Utrecht as the most
“interesting” plant of the year. The hybrid was not reported from Japan until 1997; this indicates that it resulted from
hybridization in the invaded range.
IMPACT
Ecosystem Impact
Fallopia japonica damages native riparian communities by reducing light availability, through the alteration of
the soil environment and through the release of allelochemicals. Soil K and Mn is greater under F. japonica than
under native vegetation. Fallopia japonica decreases soil bulk density and increases organic matter content,
water content and nutrient levels. It affects other trophic levels: the biomass of green frog Rana clamitans was
found to be negatively related to F. japonica cover.
Health and Social Impact
Unknown.
Economic Impact
Prolific rhizome and shoot growth can damage foundations, walls, pavements, and drainage works, and causes
flood hazards by increasing resistance to water flow and damaging flood prevention structures. Knotweeds are
an excellent food source for honeybees. Young shoots are consumed in its native range and North America.
Secondary compounds isolated from F. japonica include the anti-cancer phytoalexin resveratrol.
MANAGEMENT
Prevention
Plant debris should not be released in the wild.
Mechanical
The combination of digging the soil surface and spraying with glyphosate is the most efficient. Fallopia
sachalinensis is the easiest to control of the three taxa, the hybrid is the most resistant.
Chemical
Biological
In the native range of Japan, the leaf-feeding chrysomelid beetle Gallerucida nigromaculata regulates F.
japonica population growth, and is under consideration as a biocontrol agent in the United Kingdom and USA.
REFERENCES
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Sciences 86:887–905
Child L, Wade M (2000) The Japanese knotweed manual. Packard Publishing, Chichester, p 123
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Author: Petr Pyšek
Date Last Modified: September 21th, 2006